Buck Study Continues to Shed Light on Deer Herd

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In the third and final year of a study measuring the effectiveness of Pennsylvania's relatively new antler restrictions for deer hunters, the Pennsylvania Game Commission is reporting that field data collected by researchers indicates that the state's buck population is getting older, and bucks tend to disperse shorter distances in habitat that isn't fragmented.

"The age composition of Pennsylvania's buck population is better now than it has been in decades," noted Calvin W. DuBrock, Game Commission Bureau of Wildlife Management director. "We've confirmed this through two years of buck study data collection and by checking deer annually at meat processors and butcher shops. The change is directly related to two years of antler restrictions and, to a lesser degree, three years of concurrent antlered and antlerless deer hunting.

"This study is documenting a shift in Pennsylvania's deer herd, one that should improve its breeding ecology and intrinsic value, as well as generate increased interest among hunters."

Launched in December of 2001, the ongoing study monitors changes in survival and age structure of bucks in the deer population caused by antler restrictions, and monitors the movements - and eventual dispersal - of bucks six to 30 months old. Study animals are captured in Clover or walk-in traps, drop nets and rocket nets in Armstrong and Centre counties. All bucks are fitted with transmitters that may be radio collars, ear-tag transmitters or global positioning system (GPS) collars. Once released, the bucks are tracked until their transmitters fall off, stop transmitting or the animal dies.

During the study's first two years, 1,173 deer were trapped by field technicians in this cooperative effort involving the Game Commission, the U.S. Geologic Survey's Pennsylvania Cooperative Fish and Wildlife Research Unit and Pennsylvania State University. However, of that total, only 415, or 35 percent, were bucks. Bucks were fitted with transmitters and ear tags; females, just ear tags.

This year, through Feb. 21, the capture crews in Armstrong and Centre counties have captured 380 deer, including 92 button bucks and 59 adult males. Trapping began the second week in January. A breakdown of the captures is: 227 in clover traps; 129 in drop nets; and 24 in rocket nets.

Although the capture crews have enjoyed considerable success this winter, both study areas sustained a significant slowdown in February because heavy snowfalls and subsequent icing limited, and in some cases, restricted, deer movements. Hot trapping areas dried up almost overnight. Crews continued to trap, but clover traps sprung by gray squirrels and an occasional wild turkey, provided most of the action. Recent warmer weather has melted snow and ice and deer movements subsequently have increased. Crews are once again catching deer, and they will continue to trap into early April.

DuBrock was quick to acknowledge the hard work and rough duty put in by members of the deer capture teams, which include Game Commission biologists and research assistants and undergraduate and graduate students from various universities.

"They work unusual hours in bitter cold weather, and when they're successful, they get to be kicked black-and-blue by deer," DuBrock said. "But they like catching deer and seem to have developed quite a tolerance for snow and ice. The Game Commission and hunters truly appreciate the dedicated effort these fine young men and women are putting in."

In each of the study's first two years, about half of the collared yearling bucks (about 18 months old) survived Pennsylvania's hunting seasons and other types of mortality such as highway collisions, exposure and disease, according to research conducted by Game Commission biologist Bret Wallingford. This is evidence that indicates hunters are not shooting bucks that don't meet the regulatory requirements.

"There certainly seems to be more older bucks running around out there after our deer seasons are over than there were two years ago," noted Dr. Christopher Rosenberry, a Game Commission biometrician who is coordinating the study for the agency. "The first year, about 95 percent of the bucks we caught were button bucks, because an overwhelming majority of the antlered deer had been taken by hunters. Now, with a similar number of bucks captured, that button buck percentage has dropped to 61.

"We are starting to see an increase in the proportion of adults in our aging sample at meat processors. But a majority of the deer are still 2.5 years old or less. This year, we should start to see more 3.5-year-old deer, which, prior to antler restrictions, constituted a small fraction of the overall statewide population."

Study results from the 2003-2004 season show that hunters took about 66 percent of the 2.5-year-olds being monitored in the study.

Prior to antler restrictions, Pennsylvania had fostered imbalanced deer populations with its traditional hunting season format that featured a two-week buck season, followed by a three-day antlerless deer season. Hunters removed excessive numbers of antlered bucks annually and left immature button bucks to fill the void. The result was whitetail populations with an unnaturally high proportion of bucks 18 months old or younger. Now, there is an increase in the number of older bucks in our deer populations, and the statewide herd is better for it.

"It's important to remember that the Pennsylvania buck population composition change-over being charted in the study was hunter-built and is hunter-supported," noted Dr. Gary Alt, Game Commission deer management section supervisor. "Our hunters have made tremendous sacrifices for the older bucks they're starting to see and to create a more natural breeding ecology in our deer populations."

The buck study also has shed considerable light on the dispersal of bucks. From a timing perspective, bucks tend to disperse from their natal areas during the spring fawning period and fall rut. The numbers that dispersed early and late in these two waves varied in the study's first two years. But in both years, about 70 percent of the collared Armstrong County bucks dispersed, compared to 45 percent of the Centre County bucks.

"The dispersal rate in spring 2003 was down, but the fall dispersal more than made up for the slow spring," said Eric Long, a research associate and Ph.D. candidate at Penn State University. "Study deer also have dispersed into neighboring counties. They are Butler, Indiana, Mifflin, Huntingdon, Snyder and Union counties. The maximum dispersal distance in the Armstrong County study area was 26 miles; in Centre County, it was 13 miles."

But most of the study bucks were not logging big miles during their dispersals, according to Dr. Duane Diefenbach, Pennsylvania Cooperative Fish and Wildlife Research Unit assistant unit leader.

"Armstrong County bucks traveled about five miles on average during dispersal, compared to the four miles logged by Centre County bucks," Dr. Diefenbach said. "This study has confirmed a pattern that deer in areas with fragmented forests, like Armstrong County, tend to disperse greater distances.

"Also, through telemetry and GPS tracking, we have found that roads can be a significant barrier to dispersing bucks. In all cases to date, study deer have reacted similarly when they encounter a major highway during dispersal. They stop, or move parallel with the highway. We believe something interesting is going on here and we hope to learn more about why these study deer have reacted in the way that they have."

Bucks equipped with GPS collars have their locations recorded every seven hours, except during the rut and hunting season, when the device logs the animal's location every 2.5 hours. GPS collars cost about $3,000 each and detach from the animal after about a year. Telemetry collars are much less expensive, but require the use of technicians to track and record locations.